1. Technical Field
The present invention relates to treatment and prevention of diseases associated with amyloid formation and deposition and/or hemorrhages.
2. Background Art
Cystatin C (or CysC), also known as γ trace, is a cysteine protease inhibitor found in all mammalian body fluids and tissues. Cystatin C is composed of 120 amino acid residues (Grubb, et al., 1984). A variant of cystatin C is the major constituent of amyloid deposited in cerebral vasculature of patients with hereditary cerebral hemorrhage with amyloidosis, Icelandic type, (HCHWA-1) resulting in hemorrhagic strokes early in life.
Cystatin C has a broad spectrum of biological roles including, but not limited to, bone resorption, modulation of inflammatory responses, stimulation of glomerular mesangial cell proliferation, modulation of neuropeptide activation and degradation, neurite proliferation, and neuronal protection and survival. Cystatin C is found in all body fluids at significant concentrations, and has particularly high levels in seminal plasma (˜50 mg/l or 3.7 μM) and cerebrospinal fluid (˜5.8 mg/l or 0.43 μM). It is a potent inhibitor of papain-like peptidases and is considered a major, general extracellular cysteine protease inhibitor. However, there is data placing cystatin C and its inhibitory activity also intracellularly.
Cystatin C has a role in Alzheimer's disease (AD). Genetic data demonstrate linkage of the cystatin C gene (CST3), localized on chromosome 20, with late-onset AD. Patients with AD, Down's syndrome, cerebral amyloid angiopathy (CAA) and hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), and normally aging individuals have amyloid in cerebral vessel walls, which is mainly composed of amyloid β (Aβ). The load of amyloid deposition in the vessel walls varies between individuals. Cerebrovascular deposits of amyloid are generally asymptomatic, but in advanced cases, they can lead to vessel rupture and hemorrhage. Progression from asymptomatic to advanced CAA reflects progressive accumulation of amyloid in vessels. However, only a small percentage of individuals with high load of CAA develop cerebral hemorrhage. Thus, in these individuals, CAA appears to be a prerequisite, but not sufficient for vessel rupture. This suggests that factors, other than the amyloid load cause the damage to the vessel walls.
Immunohistochemical studies of brains of patients with AD, Down's syndrome, CAA and HCHWA-D, reveal the co-localization of cystatin C with Aβ predominantly in amyloid-laden vascular walls, and in senile plaque cores of amyloid. It has been advanced that cystatin C deposition occurs secondarily to Aβ and increases the propensity to cerebral hemorrhages. While high Aβ load was found to be a risk factor for the occurrence of hemorrhage, strong cystatin C immunostaining was a risk factor for both occurrence and enlargement of the hemorrhage, and tendency to have recurrent strokes. Thus, cystatin C can be a factor contributing to hemorrhage in patients with Aβ amyloid deposits in cerebral vasculature.
In vitro analysis of the association between cystatin C and β amyloid precursor protein (βAPP) reveal binding between the two proteins and that this binding does not affect the level of Aβ secretion. Transgenic mice have been created that express either human wild type or the HCHWA-I variant cystatin C under control sequences of the human cystatin C gene. Analysis of Aβ40 and Aβ42 concentrations in the brain of these mice show no difference between transgenic mice and their non-transgenic littermates. Thus, in vivo over expression of human cystatin C does not affect Aβ levels in mice that do not deposit Aβ.
Furthermore, cystatin C binding to Aβ was demonstrated, and this binding inhibits fibril formation. Assays using a GST-Aβ fusion protein and media of cells transfected with either wild type or variant cystatin C genes reveal binding of cystatin C to the fusion protein. Analysis of the association of cystatin C and Aβ by ELISA demonstrates that cystatin C interacts with both Aβ40 and Aβ42 in a concentration dependent manner at physiologic pH and temperature. Specific, saturable, and high affinity binding between cystatin C and Aβ has been observed. Electron microscopical analysis of fibril formation reveals that incubation of cystatin C with Aβ inhibits Aβ fibril formation in a concentration dependent manner.
As a result of crossing cystatin C transgenic mice with transgenic mice over expressing βAPP, studies for the role of cystatin C in AD and CAA have been accomplished. Specifically, a transgenic mouse expressing βAPP driven by neuron-specific Thy1.1 transgenesis cassette (APP23) can be used to study these diseases. These mice demonstrate age dependent deposition of Aβ in the neuropil as well as in cerebral blood vessels. The level of CAA in these mice increases extensively upon aging. Incidences of hemorrhages occur in very old mice. Amyloid deposition in the neuropil also occurs in the brains of Tg2576 transgenic mice, however, CAA occurs to a lesser degree. Studies have demonstrated significant decrease in plaque load in the brains of double positive mice for the cystatin C and βAPP genes compared with mice single positive for the βAPP gene. This demonstrates in vivo inhibition of amyloid fibril deposition.
In addition, using Western blot analysis it has been found that a clear difference exists in mobility of cystatin C from brain homogenates between controls and patients with different stages of AD, including patients with mild cognitive impairment (CDR 0.0-0.5). Using anti-cystatin C antibody, it has been discovered that in addition to the monomeric 14 kDa cystatin C, a band of about 20 kDa only in control individuals exists. A band of the same molecular weight was stained also with anti-Aβ antibody only in control brains, suggesting that this band can be cystatin C bound to Aβ. This suggests that cystatin C can also be used as a marker differentiating disease cases and controls. The fact that there is a difference in a very early stage of the disease is particularly important, because of the need in a method for early detection of the disease.
Immunohistochemical studies of brains of individuals with AD, Down's syndrome, CAA, and HCHWA-D, have also revealed the co-localization of cystatin C with Aβ predominantly in amyloid-laden vascular walls, and in senile plaque cores of amyloid. The risk of cerebral hemorrhage increases when high levels of cystatin C are co-deposited with Aβ in cerebrovascular amyloid deposits. There are at least two indications that cystatin C is present in amyloid deposits composed of amyloid proteins, other than Aβ. An immunohistochemical study of the brain of a patient with familial cerebral amyloid angiopathy, British type, reveals staining with anti-cystatin C antibody, suggesting that cystatin C co-deposits with the amyloid peptide. Furthermore, there is data showing staining with anti-cystatin C antibodies of amyloid deposits in patients with prion deposits such as GSS or CJD. Thus, cystatin C is a factor contributing to hemorrhage in patients with a variety of amyloid deposits in cerebral vasculature.
Furthermore, high concentrations of cystatin C cause hemorrhages in the absence of fibrillar deposits. High systemic concentrations of cystatin C were found in several human diseases, including diabetic nephropathy, hypertension, coronary heart disease and obesity, all conditions that are risk factors for intracerebral hemorrhage. The relationship between elevated circulatory cystatin C concentration and the risk for hemorrhage is supported by the occurrence of hemorrhages in cystatin C transgenic mouse lines, generated in the laboratory. Thus, cystatin C can also contribute or cause stroke, in the absence of amyloid deposition.
Accordingly, there is a need for a method and composition for inhibiting amyloid fibril formation. Amyloid fibril formation is inhibited by cystatin C or other similar peptide. Therefore, there is also a need for compositions that mimic cystatin C or a fragment of cystatin C capable of inhibiting or preventing fibril formation and/or deposition. Additionally, there is a need for a substance, composition, and method of treatment for preventing and/or treating hemorrhages.